Android APIs
public class

BackupDataOutput

extends Object
java.lang.Object
   ↳ android.app.backup.BackupDataOutput

Class Overview

Provides the structured interface through which a BackupAgent commits information to the backup data set, via its onBackup() method. Data written for backup is presented as a set of "entities," key/value pairs in which each binary data record "value" is named with a string "key."

To commit a data record to the backup transport, the agent's onBackup() method first writes an "entity header" that supplies the key string for the record and the total size of the binary value for the record. After the header has been written, the agent then writes the binary entity value itself. The entity value can be written in multiple chunks if desired, as long as the total count of bytes written matches what was supplied to writeEntityHeader().

Entity key strings are considered to be unique within a given application's backup data set. If a backup agent writes a new entity under an existing key string, its value will replace any previous value in the transport's remote data store. You can remove a record entirely from the remote data set by writing a new entity header using the existing record's key, but supplying a negative dataSize parameter. When you do so, the agent does not need to call writeEntityData(byte[], int).

Example

Here is an example illustrating a way to back up the value of a String variable called mStringToBackUp:

 static final String MY_STRING_KEY = "storedstring";

 public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
         throws IOException {
     ...
     byte[] stringBytes = mStringToBackUp.getBytes();
     data.writeEntityHeader(MY_STRING_KEY, stringBytes.length);
     data.writeEntityData(stringBytes, stringBytes.length);
     ...
 }

See also:

Summary

Public Methods
int writeEntityData(byte[] data, int size)
Write a chunk of data under the current entity to the backup transport.
int writeEntityHeader(String key, int dataSize)
Mark the beginning of one record in the backup data stream.
[Expand]
Inherited Methods
From class java.lang.Object

Public Methods

public int writeEntityData (byte[] data, int size)

Added in API level 8

Write a chunk of data under the current entity to the backup transport.

Parameters
data byte: A raw data buffer to send
size int: The number of bytes to be sent in this chunk
Returns
int the number of bytes written
Throws
IOException if the write failed

public int writeEntityHeader (String key, int dataSize)

Added in API level 8

Mark the beginning of one record in the backup data stream. This must be called before writeEntityData(byte[], int).

Parameters
key String: A string key that uniquely identifies the data record within the application. Keys whose first character is ＀ or higher are not valid.
dataSize int: The size in bytes of this record's data. Passing a dataSize of -1 indicates that the record under this key should be deleted.
Returns
int The number of bytes written to the backup stream
Throws
IOException if the write failed